Windshield wiper motor with molded sleeve and thrust elements

ABSTRACT

A method and apparatus for forming and mounting a sleeve and a thrust member in a bore in a motor/gear drive housing shaft to support the motor/gear drive shaft against radial and axial movement. Gates are formed in the motor/gear drive housing and communicate with separate first and second bores in the housing. A mold core is inserted into the housing and closes off one bore to allow the injection of molten plastic into a cavity formed between the tip end portion of the mold core and the first bore to form an annular sleeve. The annular sleeve has an inner diameter larger than the outer diameter of the end tip portion of the motor/gear drive shaft to be nominally spaced from the outer diameter of the drive shaft, but is supportingly engaged by the drive shaft under radial deformation of the drive shaft. Insertion of the drive shaft into the housing causes the tip end portion of the drive shaft to sealing close the second bore in the housing allowing the injection of molten plastic into the second bore to form a thrust member axially engaged with the end of the drive shaft to resist axial movement of the drive shaft during operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to motor and gearbox drivesand, more specifically, to motor and gearbox drives with right-angledgearboxes and, even more specifically, to motor and gearbox drives forvehicle windshield wipers.

2. Description of the Art

Electric motors having gear reduction are widely employed for manyindustrial applications. Typically, the gear reduction is provided by agear train formed of at least two meshing gear members, one of which isdriven by the motor output shaft and may be actually incorporated intothe structure of the motor output shaft, and the second fixed on an axleor shaft thereby rotating the shaft upon rotation of the motor outputshaft.

In a typical application of such a motor/gearbox drive, windshield armsand blades are attached to a conventional linkage which includes a crankarm fixedly mounted on the rotatable output shaft of a motor/gear drive.Within the motor/gearbox housing, a worm gear is formed on the motoroutput shaft. One end of the shaft is rotatably mounted in a bore formedin the housing. An intermediate end of the shaft is also supported in abearing mounted in the housing.

Cost reduction in the motor/gearbox drive has focused on the worm gearshaft and related components. Cost reduction can be achieved in thisarea by using a smaller diameter worm gear shaft. However, withoutsupport at the end of the shaft, the gear train fails at less than therequired torque output. Such failure is a result of excessive deflectionof the worm gear shaft. To control the deflection of the shaft, abearing surface is required at the end of the shaft. A thrust bearingsurface is also required to control axial movement of the shaft. Onesolution is to machine a bore in the housing, which then receives apress-in bearing. However, the location of the machined bore cannot beheld to the necessary tolerance for proper location of thebearing-to-shaft journal. Proper location of this journal is essentialfor low noise and high efficiency of the motor/gearbox drive. If thebearing is more than a few thousandths of an inch out of position,excessive noise and friction result.

Axial end play of the gear shaft must also be controlled by minimizingsuch axial movement in order to prevent noise. It is known to provide adrilled and tapped bore in the housing axially in line with the wormgear shaft, which bore receives a threaded screw carrying a moldedelastomer or resilient end cap. The screw is threaded into the tappedbore a sufficient distance to bring the end cap into engagement with theshaft. While this minimizes axial movement of the shaft to a certainextent, such an arrangement introduces other problems, the mostsignificant of which is the drilled bore which forms a new water pathentry into the motor/gearbox housing. In addition, the end cap appliesforce to the shaft and thereby controls the gear meshing.

Another solution to the radial and axial movement problems associatedwith a smaller diameter worm gear shaft is to provide another bearing inthe gearbox housing to support the end of the shaft. However, thisintroduces an added cost into the motor gearbox drive.

Thus, it would be desirable to provide a motor/gearbox drive havingmolded sleeve and thrust elements or bearing surfaces which enable asmaller than normal diameter output drive shaft to be employed whilestill preventing excess radial deflection and excess axial movement ofthe drive shaft. It would also be desirable to provide such thrust andsleeve elements which minimize noise during operation of the motor/geardrive. It would also be desirable to provide sleeve and thrust bearingsurfaces for a motor gear drive which can be easily integrated withexisting motor/gearbox production methods for low manufacturing costs.

SUMMARY OF THE INVENTION

The present invention is a unique method and apparatus for providing asleeve and a thrust member in a motor/gearbox housing to support themotor/gear drive shaft against radial and axial loads.

The apparatus includes a motor/gear drive arrangement where a motordrive shaft has a worm gear carried thereon and a tip end terminating inan end wall, and a bore is formed in a gearbox housing coaxial with theoutput shaft.

In one aspect, the invention comprises an improvement including anannular sleeve concentrically disposed about the tip end portion of theoutput shaft and nominally spaced from the tip end portion. The tip endportion of the drive shaft, under radial loads acting on the driveshaft, engages the sleeve, with the sleeve limiting further radialmovement or deflection of the drive shaft.

In another aspect of the invention, an injection molded thrust member isdisposed in the bore in the housing in coaxial registry with the endwall of the shaft. The engagement of the thrust member with the end wallof the output shaft prevents axial movement of the drive shaft.

According to one aspect of the invention, at least one and preferablyeach of the sleeve and the thrust member are formed by injectionmolding. More specifically, the sleeve and tubular member are eachinjection molded within the housing during the assembly of themotor/gear drive.

The sleeve preferably has an inner diameter which is nominally largerthan the outer diameter of the tip end portion of the drive shaft suchthat the tip end portion of the drive shaft nominally rotates within thebore in the sleeve during normal operation of the drive shaft.

Another aspect of the present invention defines a unique method ofmanufacturing a motor/gear drive wherein the motor has a drive shaftcarrying a worm gear, and a tip end portion terminating in an end wall,the method comprising:

forming a bore in a housing surrounding the motor/gear drive, the borehaving a first bore portion of a first diameter; and

forming a sleeve having a through bore in the first bore portion of thehousing.

The sleeve is preferably formed by the steps:

forming a shoulder between the first bore portion and a second boreportion;

forming a first gate in the housing communicating with the first boreportion; and

inserting a mold core into the housing, the mold core having a first endportion with a diameter larger than the outer diameter of the tip endportion of the drive shaft and a second larger diameter portion having ashoulder formed between the first and second portions sealingly closingthe first bore portion, the first bore portion and the tip end portionof the mold core forming an interior cavity;

injecting molten plastic into the interior cavity through the first gateto form the sleeve having an inner diameter surface surrounding a bore;and

removing the mold core.

The method also includes forming a shoulder on the mold core which isengagable with a bearing mounting surface in the housing toconcentrically align the mold core with the first and second boreportions in the housing to concentrically align the sleeve with thefirst bore portion.

In yet another aspect, a first flange is formed on the housing and isengaged with a mating flange formed on the mold core. Engagement of thetwo flanges aligns the later formed sleeve concentrically about alongitudinal axis of the drive shaft when the drive shaft is engagedwith the sleeve.

In yet another aspect of the present invention, the method furthercomprises the steps of:

forming a second gate in the housing communicating with the second boreportion;

forming an end wall of the drive shaft with an outer diameter largerthan the diameter of the second bore portion;

disposing the end wall of the drive shaft to sealingly close off an endof the second bore portion;

inserting the drive shaft of the motor/gear drive into the housing withthe tip end portion of the drive shaft extending through the first boreportion;

disposing the end wall of the drive shaft to sealing close the secondbore portion; and

injecting molten plastic through the second gate into the second boreportion to form a thrust member in the second bore portion in registrywith the end wall of the drive shaft.

The unique thrust member and sleeve of the present inventionmanufactured by the unique inventive method enables a smaller diameterand therefore a lower cost motor/gear drive shaft carrying a worm gearto be rotatably mounted in a housing and supported against radial andaxial movement for reduced noise and friction.

The unique sleeve and thrust member of the present invention alsocontribute to a reduced manufacturing cost for the motor/gear drivesince a costly bearing is not required to support the end portion of themotor/gear drive shaft. Further, the sleeve and thrust member areuniquely formed by an injection molding process utilizing gates formedin the motor/gear drive housing. This reduces assembly steps and partcount. In addition, the injection molding of the sleeve and the thrustmember can be integrated into an existing motor/gear drive assemblyprocess for a simplified manufacturing of the motor/gear drive.

The use of separate gates directed to separately closed bore portions inthe housing used to form the sleeve and thrust member, respectively,enable different materials to be used to form the sleeve and the thrustmember thereby enabling the materials to be engineered to meet thedifferent radial and/or axial loads of the sleeve and the thrust member.

BRIEF DESCRIPTION OF THE DRAWING

The various features, advantages and other uses of the present inventionwill become more apparent by referring to the following detaileddescription and drawing in which:

FIG. 1 is a longitudinal cross-sectional view through a gearbox of amotor gear drive having sleeve and thrust bearing surfaces constructedin accordance with the teachings of the present invention and apparatus;

FIG. 2 is a partial, cross-sectional view through one end of the gearboxshown in FIG. 1;

FIG. 3 is an enlarged longitudinal cross-sectional view of a gearboxshowing the mounting of a mold core of the present invention in thegearbox shown in FIG. 1;

FIG. 4 is a partial, cross-sectional view of the end of the gearboxhousing, with the sleeve of the present invention mounted therein;

FIG. 5 is a partial, cross-sectional view of the end portion of the gearhousing shown in FIG. 4, with the gear shaft mounted therein, prior tothe formation of the thrust bearing surface according to the presentinvention; and

FIG. 6 is a partial, cross-sectional view of the end portion of the gearhousing shown in FIGS. 4 and 5, with the gear shaft mounted therein,showing a gap between the end portion and the sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, and to FIG. 1 in particular, there isdepicted a portion of a motor/gear drive suitable for use in manydifferent applications. It will be understood that although thefollowing detailed description and the drawing show the inventivefeatures of the motor/gear drive in a windshield wiper driveapplication, the present invention may also be employed in anymotor/gear drive having an angled gearbox and, more preferably, aright-angled gearbox incorporating a gear pair, such as meshing worm andworm gear.

FIG. 1 depicts only the motor shaft 10, with the drive motor itself notbeing shown. In this application, the motor and gear drive are mountedin two separate housings with a housing 12, which is typically a casthousing, by example only, formed of a suitable metal, such as aluminum,depicted for the gear drive.

The shaft 10 has a generally cylindrical configuration for a portion ofits length extending outward from the motor itself. In this application,a helical worm gear 14 is integrally formed in the output shaft 12 bymolding or machining. The worm gear 14 is spaced a short distance from atip end portion 16 of the shaft 10. The tip end portion 16 terminates inan end wall 18.

An intermediate portion of the shaft 10 is supported in the housing 12by a pair of bearing races 20 and 22. The bearing races 20 and 22 areheld in position in the housing 12 by a bearing housing 24 in contactwith the inner bearing race 20 and a sleeve 26 and clip 28 which aredisposed in engagement with the outer race 22.

The clip 28 seats within an undercut 30 in the shaft to retain thesleeve 26 in position in a intermediate bore formed in the housing 12.

It will be understood that the worm wheel or worm which engages the wormgear 14 and is fixedly mounted on a drive shaft, not shown in FIG. 1, isangularly offset, typically at 90° from the axis of the drive shaft 10.

In order to use a smaller diameter shaft 10 so as to reduce the cost ofthe motor/gear drive, the tip end portion 16 of the shaft 10 must besupported against radial forces which tend to deflect the drive shaft 10as well as axial thrust forces tending to move the shaft 10 axiallywithin the housing 12. A unique solution to this problem is provided bythe present invention in low cost manner which can also be easilyintegrated in the assembly process of the motor/gear drive.

According to the present method and apparatus, a unique annular sleeve32 and a unique thrust member or surface 34 are provided in the housing12 and positioned to resist radial deflection of the tip end 16 of theshaft 10 as well as axial movement of the shaft 10 under operatingthrust loads.

According to one aspect of the present invention, the sleeve 32 isformed as an annular member having an outer diameter and an innerdiameter formed to certain dimensions as described hereafter. The sleeve32 is formed of a suitable material which provides high durability andwhich minimizes noise when engaged by the shaft 10.

According to a unique feature of the present invention, the innerdiameter of the sleeve 32 is slightly oversized or larger than the outerdiameter of the tip end portion 16 of the shaft 10. This provides radialspacing which allows the tip end 16 of the shaft 10 to freely rotatewithin the sleeve 32 and without contacting the inner diameter surfaceof the sleeve 32 during normal operation (as best seen in FIG. 6).However, when excessive radial forces are exerted on the shaft 10, thetip end portion 16 of the shaft 10 will flex bringing the outer diameterof the tip end portion 16 into engagement with the inner diameter of thesleeve 32. The sleeve 32 resists further radial movement or deflectionof the tip end 16 of the shaft 10 so as to support the shaft and reducenoise and friction during rotation of the shaft 10.

The thrust member 34 is provided in a bore in the housing 12, asdescribed hereafter, coaxially with the shaft 10 and in registry withthe end wall 18 of the shaft 10 as shown in FIG. 1. The thrust member 34engages, but does not load the shaft 10, so as to merely prevent axialmovement of the shaft 10 when thrust forces are exerted on the shaft 10such as forces which occur at the reversal or inwipe and endwipepositions of a windshield wiper arm assembly.

The sleeve 32 and thrust member 34 are formed of suitable plasticmaterials which can be engineered to optimize the required properties ofdurability and noise suppression. The materials forming the thrustmember 34 and the sleeve 32 may be the same or different as the sleeve32 and the thrust member 34 serve different functions.

According to another aspect of the present invention, the sleeve 32 andthe thrust member 34 are formed according to a unique method which willnow be described.

As shown in FIG. 2, the housing 12 has a stepped bore 40 formed of afirst larger diameter bore portion 42 and a second, coaxial smallerdiameter bore portion 44, with both of the first and second boreportions 42 and 44 referred to hereafter simply as the first bore 42 andthe second bore 44. A first gate or runner 46 is formed through thehousing 12 and has an outlet disposed in fluid communication with thefirst bore 42 and an inlet opening externally with respect to thehousing 12. The first gate 46 when molded defines means for preventingrotation of the sleeve 32 with respect to the housing 12, and isdesigned to provide a path for molten plastic, as described hereafter,during an injection molding process to flow into the first bore 42.

The second bore 44 communicates with a second gate or runner 48 whichalso extends through the housing 12 from an inlet. The second gate orrunner 48 when molded defines means for preventing rotation of thethrust bearing 34 with respect to the housing, and provides a flow pathfor molten plastic during an injection molding process step to thesecond bore 44 as described hereafter.

The present method and apparatus make use of a mold core 50, shown inFIG. 3 which concentrically aligns, seals and forms an interior cavityfor forming the sleeve 32 as described hereafter. The mold core 50includes a shank 52 having a first diameter cylindrical end portion 54,an adjacent second, larger diameter cylindrical portion 56, an adjacentyet larger diameter cylindrical portion, and a final largest diameterportion 60.

The cylindrical portions 54, 56, and 60 serve various functions.Specifically, the first cylindrical portion 54 of the mold core 50 hasan outer diameter just slightly smaller than the inner diameter of thesecond bore 44 in the housing 12 so as to fit therein. A first shoulder62 is formed between the coplanar ends of the first and secondcylindrical portions 54 and 56 of the mold core 50. The first shoulder62 is designed to sealingly engage a face 64 formed between the firstand second bores 42 and 44 in the housing 12.

Similarly, a second shoulder 66 is formed between the ends of the secondcylindrical portion 56 and the third cylindrical portion 58 of the moldcore 50. The second shoulder 66 is positioned to sealingly engage asecond face 68 formed in the housing 12 at the end of the first bore 42and an enlarged internal cavity formed within the housing 12. The firstshoulder 62 and the first face 64 combine with the second shoulder 66and the second face 68 to sealingly close off and form an interiorchamber 70 within the first bore 42 of the housing 12 between the innersurface of the first bore 42 and the outer surface of second cylindricalportion 56 of the mold core 50. The interior cavity 70 is disposed influid flow communication with the first gate or runner 46 to enablemolten plastic to be injected into the interior cavity 70 to form thesleeve 32 as shown in FIGS. 1 and 4.

It should also be noted that the outer diameter of the secondcylindrical portion 56 of the mold core 50 has a larger diameter thanthe outer diameter of the tip end portion 16 of the shaft 10. Thisenables the inner diameter of the sleeve 32 formed in the cavity 70 tobe larger than the outer diameter of the end tip portion 16 of the shaft10 so as to be nominally spaced from the tip end portion 16 of the shaft10.

A third shoulder 72 is formed intermediate along the shank 52 of themold core 50 and is positioned to engage a third face 74 formedintermediately within the housing 12. The third face 74 is formed as onesupport wall of the outer bearing race 22 shown in FIG. 1. An enlargedannular flange 78 is formed on the mold core 50 and extends radiallyoutward from an intermediate portion of the shank 52. The annular flange78 is formed with an outer cylindrical mounting flange 76 which isadapted to engage a similar mounting flange on a portion of the housing12.

The mating engagement of the various shoulders, flanges and faces on themold core 50 and the housing 12 cause the first cylindrical portion 54of the mold core 50 to be coaxially aligned with what will be theposition of the motor output shaft 10 to ensure a properbearing-to-shaft journal which is essential for low noise and highefficiency.

After the injected plastic cools to a hardened state forming the sleeve32, the mold core 50 is removed as shown in FIG. 4. In the next methodstep of the present invention, the drive shaft 10 extending outward fromthe motor, not shown, is aligned with the interior bore 33 within thesleeve 32. The tip end portion 16 of the shaft 10 is then inserted intothe bore 33 in the sleeve 32 as shown in FIG. 5. The tip end portion 16seats against the first face 64 closing off the second bore 44 from thefirst bore 42 containing the sleeve 32. Molten plastic is then injectedthrough the second gate 48 into the first bore 44 to form the thrustmember 34, as shown in FIG. 5. The thrust member 34 engages the end wall18 of the tip end portion 16 of the shaft 10 to hold the shaft 10 fromaxial movement under any axial forces exerted on the shaft 10 duringoperation of the motor and gear.

In summary, there has been disclosed a unique method and apparatus forforming and mounting a sleeve and thrust member in a bore axiallydisposed with respect to the longitudinal axis of a motor/gear driveshaft carrying a worm gear, which sleeve and thrust member minimizeradial deflection and axial movement of the drive shaft thereby reducingnoise and friction. The sleeve and thrust member are uniquely formed byinjection molding in the motor/gearbox housing for a reducedmotor/gearbox manufacturing cost while still providing long-termdurability. The injection molding process steps of the present inventionare integrated into the existing motor/gearbox assembly process tofurther reduce the cost of the motor/gearbox drive.

What is claimed is:
 1. In a motor/gear drive having a shaft with a wormgear carried thereon and a free tip end portion with an outer diameterterminating in an end wall, and a housing having a bore formed coaxialwith respect to the shaft to be installed therein, the improvementcomprising: a plastic annular sleeve within the bore of the housingconcentrically disposed to be positionable about the outer diameter ofthe tip end portion of the shaft to be installed and to be nominallyspaced radially from the outer diameter of the tip end portion, andwherein the sleeve is operable to supportingly engage the outer diameterof the tip end portion of the shaft only in response to radial loadsacting to deflect the shaft into contact with the annular sleeve; adiscrete plastic thrust member within the bore of the housing disposedto be in coaxial registry with the end wall of the shaft to beinstalled, and operable to be in engagement with the end wall of theshaft to be installed to prevent axial movement of the shaft; whereinthe plastic thrust member is an injection molded thrust member formed insitu within the bore of the housing; and wherein the outer diameter ofthe tip end portion of the shaft to be installed is larger than adiameter of the thrust member engageable with the end wall of the tipend portion of the shaft.
 2. The improvement of claim 1 furthercomprising: the sleeve having a bore extending therethrough, the borehaving an inner diameter larger than the outer diameter of the tip endportion of the shaft to be installed.
 3. The improvement of claim 1;further comprising: the thrust member being injection molded afterinstallation of the shaft, wherein a portion of the end wall of theshaft defines at least a portion of a chamber to receive injectedplastic forming the thrust member during injection molding.
 4. Theimprovement of claim 1 further comprising: the bore having a firstportion of a first diameter and an axially endmost, coaxial, secondportion of a smaller diameter, a shoulder formed between the first andsecond portions, and a first gate formed in the housing communicatingwith the first portion.
 5. The improvement of claim 4 furthercomprising: a second gate formed in the housing communicating with thesecond portion.
 6. The improvement of claim 1 further comprising: meansfor preventing rotation of the plastic annular sleeve with respect tothe housing.
 7. The improvement of claim 6 wherein the rotationpreventing means further comprises a gate formed integral with theplastic annular sleeve through the housing.
 8. The improvement of claim1 further comprising: means for preventing rotation of the plasticthrust member with respect to the housing.
 9. The improvement of claim8, wherein the rotation preventing means further comprises a gate formedintegral with the plastic thrust member through the housing.
 10. In amotor/gear drive having a shaft with a worm gear carried thereon and afree tip end portion with an outer diameter terminating in an end wall,a housing having a bore formed coaxial with respect to the shaft to beinstalled therein, the improvement comprising: a plastic thrust memberand a separate and distinct plastic annular sleeve formed within thebore of the housing, the plastic thrust member disposed to be in coaxialregistry with the end wall of the shaft to be installed, and operable tobe in engagement with the end wall of the shaft to be installed toprevent axial movement of the shaft; wherein the plastic thrust memberis an injection molded thrust member formed in situ within the bore ofthe housing; and wherein the outer diameter of the tip end portion ofthe shaft to be installed is larger than the diameter of the thrustmember engageable with the end wall of the tip end portion of the shaft.11. The improvement of claim 10 further comprising: means for preventingrotation of the plastic annular sleeve with respect to the housing. 12.The improvement of claim 11 wherein the rotation preventing meansfurther comprises a gate formed integral with the plastic annular sleevethrough the housing.
 13. The improvement of claim 10 further comprising:means for preventing rotation of the plastic thrust member with respectto the housing.
 14. The improvement of claim 13 wherein the rotationpreventing means further comprises a gate formed integral with theplastic thrust member through the housing.
 15. A motor/gear drivehousing for enclosing a shaft supporting a worm gear for engagement witha pinion gear, the shaft having one end connectible to a prime mover anda free tip end portion with an outer diameter terminating in an endwall, the motor/gear drive housing comprising: at least one peripheralwall defining an enclosed area with at least one open side, at least oneaperture formed within the peripheral wall and engageable to encirclepart of the free tip end portion of the shaft to be installed; at leastone injection molded plastic annular sleeve formed in situ within theaperture and having an inner diameter positionable to encircle the freetip end portion of the shaft to be installed therethrough with at leastsome clearance therebetween, such that the annular sleeve is operable tosupportingly engage the outer diameter of the free tip end portion ofthe shaft only in response to radial loads acting to deflect the shaftinto contact with the annular sleeve; and a discrete injection moldedplastic thrust member formed in situ within the at least one aperture ofthe housing, the thrust member disposed to be in coaxial registry withthe end wall of the shaft to be installed, and operable to be engageablewith the end wall of the shaft to be installed to prevent axial movementof the shaft, the outer diameter of the free tip end portion of theshaft to be installed being larger than a diameter of the thrust memberengageable with the end wall of the free tip end portion of the shaft,the thrust member injection molded after installation of the shaft,wherein a portion of the end wall of the shaft defines at least aportion of a chamber to receive injected plastic forming the thrustmember during injection molding.
 16. The motor/gear drive housing ofclaim 15 further comprising: means for preventing rotation of theplastic annular sleeve with respect to the housing.
 17. The motor/geardrive housing of claim 16 wherein the rotation preventing means furthercomprises a gate formed integral with the plastic annular sleeve throughthe housing.
 18. The motor/gear drive housing of claim 15 furthercomprising: means for preventing rotation of the plastic thrust memberwith respect to the housing.
 19. The motor/gear drive housing of claim18 wherein the rotation preventing means further comprises a gate formedintegral with the plastic thrust member through the housing.
 20. In amotor/gear drive housing for enclosing a shah supporting a worm gear forengagement with a pinion gear, the shaft having one end connectible to aprime mover and a free tip end portion with an outer diameterterminating in an end wall, the housing having an aperture formedcoaxial with respect to the shaft to be installed therein, theimprovement comprising: a discrete plastic injection molded annularsleeve and a discrete plastic injection molded thrust member formed insitu within the aperture of the housing, wherein the plastic annularsleeve is positionable to be coaxially sheathing the outer diameter ofthe free tip end portion of the shaft to be installed and to benominally spaced radially from the outer diameter of the free tip endportion, the sleeve operable to supportingly engage the outer diameterof the free tip end portion of the shaft only in response to radialloads acting to deflect the shah into contact with the annular sleeve,wherein the plastic thrust member is positionable to be in coaxialregistry with the end wall of the shaft, and operable to be engageablewith the end wall of the shaft to prevent axial movement of the shaft;and wherein the outer diameter of the tip end portion of the shaft to beinstalled is larger than a diameter of the thrust member engageable withthe end wall of the tip end portion of the shaft.
 21. The improvement ofclaim 20 further comprising: means for preventing rotation of theplastic annular sleeve with respect to the housing.
 22. The improvementof claim 21 wherein the rotation preventing means further comprises agate formed integral with the plastic sleeve through the housing. 23.The improvement of claim 20 further comprising; means for preventingrotation of the plastic thrust member with respect to the housing. 24.The improvement of claim 23 wherein the rotation preventing meansfurther comprises a gate formed integral with the plastic thrust memberthrough the housing.